When Jack was young, he began inflicting harm on animals. It started with just pulling the wings off flies, but eventually progressed to torturing squirrels and stray cats in his neighbourhood.

As an adult, Jack found that he did not get much thrill from harming animals, so he began hurting people instead. He has killed 5 homeless people that he abducted from poor neighbourhoods in his home city. Their dismembered bodies are currently buried in his basement.

Now, knowing what I have just told you about Jack, is it more probable that Jack is: A) A teacher. Or B) A teacher who does not believe in God?

Domenico Ghirlandaio, Commissioning of the Twelve Apostles (1481), from the Sistine Chapel.

If you answered “B”, you would not be alone. An average of 50 percent of people in a recent suite of experiments gave the same answer. The wrong answer.

Wrong not because Jack believes in God - we have no way of knowing what Jack believes. B is necessarily incorrect because the entirety of group “B” the teachers who don’t believe in God, are also members of group “A”, the teachers. It is impossible for B to be more likely than A, but it is likely that a great many people in group A do not belong to B.

The question about Jack exploits the conjunction fallacy by which additional detail makes a scenario seem intuitively more likely. Amos Tversky and Daniel Kahneman showed that people make this mistake by applying a simple rule called the “representativeness heuristic”; additional detail that seems to match the description biases people toward believing that the detailed option is more likely.

Which makes exercises like the question about Jack an interesting tool with which to study the intuitions people harbour about certain groups.

That’s exactly what the University of Kentucky’s Will M. Gervais did in a recent paper in PLoSONE. He presented subjects with stories of heinous moral transgressions: the one above, one involving incestuous relations between adult siblings, and one particularly imaginative scenario involving a man “making love” to a chicken carcass before roasting it. (Don’t worry, the man used a condom and fully sterilized the carcass before roasting it).

Subjects, after reading one of these scenarios, were then asked to make a choice in a conjunction fallacy exercise. Some subjects, under option B, were given the conjunction “… does not believe in God” that I presented in the example above. Others, however, were presented with conjunctions specifying that the morally suspect protagonist was Jewish, Christian, Muslim, Hindu or Buddhist.

The experiment amounts to a comparison of how many subjects made the conjunction fallacy with each group. People make the conjunction fallacy more readily when the additional detail confirms their prior biases about the group involved.

Only 5-20 percent of subjects made the conjunction fallacy with any of the religious groups. Not many people felt a religious descriptor matched neatly with the description of the moral transgression being presented.

But fully half of all subjects fell for the fallacy when the morally suspect person was described as not believing in God. Clearly there is a near-unshakable intuition among much of the public that atheists are morally bereft.

That’s no surprise. The outwardly devout often express disbelief that without a celestial policeman or the threat of eternal damnation or some such, there can be any morality. Gervais opens his paper with a pithy quote to this effects from Dostoevsky’s The Brothers Karamazov:

Without God and the future life? It means everything is permitted now, one can do anything?

Of course that isn’t true: a lack of belief does not necessarily mean that anything goes. But the relative morality of atheists and believers is a subject for another day. What matters here - particularly for atheists - is the overwhelming tendency for people to associate amorality with atheism. A fascinating Pew Centre report showed that world-wide, people tend to hold the opinion that belief is essential to morality.

Believers mistrust atheists and their unconcern for the afterlife. I’ve written before about Will Gervais’ research with Ara Norenzayan showing that this distrust can be ameliorated by gently reminding believers of the existence of secular authorities like the police. The rise in effective secular institutions of justice may well be part of slow dwindling of religious devotion in much of the world.

But the conviction that faith is not only a virtue itself but the source of virtue is a gift that keeps on giving for religions, their leaders, and the politicians who wear their faith on their sleeves. Misconstruing secularists and atheists has long been political sport in the U.S.A. George H.W. Bush, for example, wore his irrational contempt for atheism as a badge of honour:

I support the separation of church and state. I’m just not very high on atheists.

Pre-formed ideas about the morality of those who don’t profess belief are also likely to be important in Australia’s ostensibly secular society. Last week’s budget pain for school and university education was accompanied, to much outrage, by a $245 million splurge on the school chaplaincy program. That decision, and the ongoing battles over Religious Instruction, Special Religious Education and ethics classes, represent part of an ongoing challenge to secularism in Australian public schools and institutions.

Atheists and humanists and various others trying to convince the world that one can be good without God and that societies benefit from secularization face the considerable obstacle of representative heuristics about atheist amorality. Unfortunately for them it isn’t just believers who hold these heuristics. Gervais took a more detailed look at the actual beliefs of his subjects, and found that even the atheists among them tended to make the conjunction fallacy more often regarding non-believers than any of the other groups.

If non-believers themselves jump to the conclusion that immoral deeds are more representative of the godless, then religion has an even bigger advantage in the turf-war over morality than previously thought.

Tim Minchin reckons we should judge people not by their group membership but by their deeds. How, though, does one overcome representativeness heuristics?